1. Field of the Invention
The present invention relates to a flow control valve for controlling flow of a coolant that is applied to the refrigeration cycle and, more specifically, to a flow control valve capable of securing reliability in operation of the valve by restraining heat exchange from a heat expansion solution in a high temperature state to a coolant in a low temperature state, thereby enhancing the expansion efficiency of a heat expansion solution.
2. Description of the Related Art
Generally, a refrigeration unit includes an evaporator, a compressor, a condenser, and an expansion valve. Such refrigeration unit lowers circumference temperature by respectively performing the refrigeration cycle consisting of evaporation, compression, condensing, and expansion strokes at the evaporator, compressor, condenser, and expansion valve.
The refrigeration cycle is described as follows.
At the evaporator, liquefied coolant supplied by the expansion valve is vaporized by taking away latent heat from surrounding air. As a result, the temperature of the surrounding air is lowered. The cooled air maintains a cooling room at a low temperature by natural convection or a blowing fan. The liquefied coolant supplied from the expansion valve and the vaporized coolant exist together in the evaporator. Here, while the coolant changes from liquid to vapor state, vapor pressure has a specific relation to vapor temperature.
Coolant in gas state that is vaporized in the evaporator is absorbed into the compressor, which maintains the inside of the evaporator at low pressure even though its temperature is very low to actively vaporize coolant remaining in the liquid state.
Meanwhile, the vaporized coolant absorbed into the compressor is compressed in the cylinder by a piston, thereby increasing its pressure so that the vaporized coolant can be easily liquefied even though it is cooled by water at room temperature or cooling air.
Thereafter, the compressed gas of the compressor is cooled and liquefied in the condensing stroke. Like the evaporation stroke, the coolant in the condensing stroke exists in both liquid and vapor states. During phase transformation from vapor state to liquid state, the condensing pressure has a specific relation to the condensing temperature.
The expansion stroke then lowers the pressure of the liquefied coolant to a state capable of easy vaporization prior to sending the liquefied coolant into the evaporator. The expansion stroke is performed by the expansion valve. Such expansion valve controls the flow of the coolant to the evaporator as well as lowering its pressure. The flow of the coolant vaporized in the evaporator determines the heat flow to be removed from the refrigeration room under a given evaporation temperature(evaporation pressure). Therefore, it is important to precisely control a supply flow of the coolant.
In summary, the expansion valve adiabatically expands liquid coolant of high temperature and high pressure into liquid coolant of low temperature and low pressure by throttling and simultaneously functions as a flow control valve for maintaining an appropriate supply flow of the coolant in accordance with the given load of the evaporator.
There are various kinds of expansion valves known of which have different modes of operation and structure. Recently, a flow control valve has been provided using both heat and air pressure, which has such characteristics that driving force is high, fine driving is possible, and fabrication cost is low.
FIG. 1 is a sectional view showing a conventional flow control valve.
Referring to FIG. 1, the conventional flow control valve includes a predetermined shaped cap 1, a bottom plate 3 of heater, in which the bottom plate 3 is made of ceramic material and has inlets 2 at both sides thereof. The conventional flow control valve also includes an aluminum(Al) electrode 5 having a heating electrode 4 placed at the central portion thereof. The Al electrode 5 is mounted on and fixed to the upper face of the bottom plate 3. A membrane 7 is mounted on and fixed to circumference of the Al electrode 5 with a spacer 6 interposed therebetween. A lower attaching layer 8 is disposed between the upper face of the Al electrode 5 and the bottom face of the spacer 6, and an upper attaching layer 9 is disposed between the bottom face of the membrane 7 and the upper face of the spacer 6, for enhancing the attaching force. A heat expansion solution 10 is filled in a space 14 formed between the Al electrode 5 and the membrane 7. A sealing bottom plate 11 is fixed to the bottom plate 3 of the heater, for sealing the inlets 2 for the heat expansion solution. The electric power lines 12 run to the Al electrode 5.
The cap 1 has a space 1a through which the coolant passes. An inlet 1b for introducing the coolant into the space 1a and an outlet 1c for exhausting the coolant from the space 1a to the outside are formed to communicate with the space 1a in the cap 1.
In order to assemble the above conventional flow control valve, an aluminum(Al) electrode 5 having a heating electrode 4 of Ta-Al alloy is fixed on the upper surface of the bottom plate 3 of the heater, and the lower attaching layer 8, the spacer 6, the upper attaching layer 9 and the membrane 7 are assembled on the Al electrode 5 in the named order such that the space 14 is formed.
Afterwards, the heat expansion solution 10 is supplied through the inlets 2 from the lower portion of the bottom plate 3 of the heater and a sealing plate 11 is attached to the lower surface of the bottom plate 3 of the heater for the sealing of the heat expansion solution inlets 2. Thereafter, the sealing plate 11 is mounted on the bottom surface of the cap 1 and is then fixed thereto. Next, the electric power lines 12 are drawn from outside of the cap 1. Finally, the central portion of the membrane 7 is placed at the direct lower portion of the outlet 1c that is formed in the cap 1.
In the above described conventional flow control valve, the liquid coolant is introduced through the inlet 1b of the cap 1, passes through the space 1a formed therein, and is then exhausted to evaporator through the outlet 1c.
When flow control of the liquid coolant is needed, a voltage is applied to the Al electrode 5 through the electric power line 12 placed at the outside of the cap 1 and accordingly the heating electrode 4 of Ta-Al emits heat. As a result, the heat expansion solution 10 is expanded, which is filled in the space bounded by the Al-electrode 5, the spacer 6, and the membrane 7. As shown in FIG. 2, by heat expansion of the heat expansion liquid 10, the central portion of the membrane 7 is swollen towards the outlet 1c of the cap 1 to control exhaust flow of the coolant through the outlet 1c, whereby total flow of the coolant is controlled.
The conventional flow control valve however has a shortcoming that heat exchange is very active since the coolant and heat expansion liquid 10 are separated only by the membrane 7.
In other words, when the electric power is applied to the Al electrode 5, the heating electrode 4 of Ta-Al alloy becomes heated and thereby heat is emitted therefrom. The emitted heat enhances temperature of the heat expansion solution 10 to a considerable degree. Since heat of the temperature-enhanced heat expansion solution 10 is transferred into the coolant of low temperature, the heat expansion solution 10 does not maintain a high temperature. Therefore, the heat expansion efficiency is lowered and flow control activity is accordingly lowered, negatively affecting the reliability of the product.